Process for producing aromatic polyimide filaments

Abstract

Aromatic polyimide fibers having an enhanced mechanical strength are produced by a process comprising the steps of: preparing a spinning dope solution of at least one aromatic polyimide having 90 molar % or more of a recurring unit of the formula (I): <IMAGE> wherein R is a divalent aromatic radical, in a phenolic solvent; converting the dope solution into at least one filamentary stream thereof; solidifying the filamentary dope solution stream by removing the solvent therefrom to provide at least one undrawn filament, and; drawing the undrawn filament at a temperature of 20 DEG to 600 DEG C. at a draw ratio of 1.5 to 5.0.

We claim: 
     
       1. A process for producing aromatic polyimide filaments, comprising the steps of: (1) preparing a spinning dope solution of a polymer material consisting of at least one aromatic polyimide having at least 90 molar % of a recurring unit of the formula (I): ##STR7##  wherein R represents a divalent aromatic radical, in a solvent comprising, as a main component thereof, at least one phenolic compound;   (2) extruding said spinning dope solution through at least one spinning hole to form at least one filamentary stream thereof,   (3) solidifying said filamentary stream of said spinning dope solution to provide at least one undrawn aromatic polyimide filament, and;   (4) drawing said undrawn filament at a temperature of from 20° to 600° C. at a draw ratio of from 1.5 to 5.0.   
     
     
       2. The process as claimed in claim 1, wherein the divalent aromatic group represented by R in the formula (I) is a residue of an aromatic diamine from which two amino groups are excluded. 
     
     
       3. The process as claimed in claim 1, wherein said aromatic polyimide has a logarithmic viscosity of from 0.3 to 7.0, determined at a concentration of 0.5 g per 100 ml of a mixture solvent of 4 parts by volume of P-chlorophenol and 1 part by volume of O-chlorophenol at a temperature of 30° C.   
     
     
       4. The process as claimed in claim 1, wherein said aromatic polyimide is a polymerization-and-imidization product of a tetracarboxylic acid component comprising at least 90 molar % of at least one biphenyl tetracarboxylic acid or its anhydride, salt or ester with a diamine component comprising at least one aromatic diamine of the formula (II):   H.sub.2 N--R--NH.sub.2                                     (II)     wherein R is as defined above.   
     
     
       5. The process as claimed in claim 4, wherein said tetracarboxylic acid component is selected from the group consisting of 3,3',4,4'-biphenyl tetracarboxylic anhydride and 2,3,3',4'-biphenyl tetracarboxylic anhydride. 
     
     
       6. The process as claimed in claim 4, wherein said tetracarboxilic acid component contains 10 molar % or less of at least one member selected from the group consisting of pyromellitic acid, 3,3',4,4'-benzophenone tetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) sulfone, bis (3,4-dicarboxyphenyl) ether, bis (3,4-dicarboxyphenyl) thioether, butane tetracarboxylic acid, and anhydrides, salts and esters of the above-mentioned compounds. 
     
     
       7. The process as claimed in claim 4, wherein said aromatic diamine is selected from the group consisting of those of the formulae (III) and (IV): ##STR8## wherein R 1  and R 2  respectively represent, independently from each other, a member selected from the group consisting of hydrogen atom, lower alkyl radicals having 1 to 3 carbon atoms and lower alkoxyl radicals having 1 to 3 carbon atoms; A represents a divalent linking member selected from the class consisting of --O--, --S--, --C--, --SO 2  --, --SO--, --CH 2  -- and --C(CH 3 ) 2  --, and m represents an integer of from 1 to 4. 
     
     
       8. The process as claimed in claim 1, wherein said phenolic compound has a melting point of 100° C. or less and a boiling point of about 300° C. or less under atmospheric pressure. 
     
     
       9. The process as claimed in claim 1, wherein said phenolic compound is selected from the group consisting of phenol, alkyl-substituted monohydric phenol compounds and halogenated monohydric phenol compounds. 
     
     
       10. The process as claimed in claim 9, wherein said alkyl-substituted monohydric phenol compound is selected from the group consisting of O-, m- and P-cresols, 3,5-xylenol, carvacrol and thymol. 
     
     
       11. The process as claimed in claim 9, wherein said monohydric halogenated phenol compound is selected from the group consisting of those of the formula (VII): ##STR9## wherein R 3  represents a member selected from the group consisting of hydrogen atom and alkyl radicals having 1 to 3 carbon atoms and X represents halogen atoms. 
     
     
       12. The process as claimed in claim 1, wherein said spinning dope solution contains 5 to 30% by weight of said polymer material. 
     
     
       13. The process as claimed in claim 1, wherein said spinning dope solution has a rotation viscosity of at least 500 centiposes at a temperature of from 0° to 150° C. 
     
     
       14. The process as claimed in claim 1, wherein said solidification is carried out by introducing said filamentary stream of said spinning dope solution into a coagulating liquid which is compatible with said solvent but not compatible with said polymer material, to coagulate said filamentary stream of said spinning dope solution. 
     
     
       15. The process as claimed in claim 14, wherein said coagulating liquid comprises at least one member selected from the groups consisting of water, lower aliphatic alcohols having 1 to 5 carbon atoms, lower aliphatic ketones having 3 to 5 carbon atoms, tetrahydrofuran, dioxane, ethyleneglycol monomethylether, dimethylacetamide, dimethylformamide and dimethylsulfoxide. 
     
     
       16. The process as claimed in claim 1, wherein said solidification is carried out by evaporating away said solvent from said filamentary stream of said spinning dope solution. 
     
     
       17. The process as claimed in claim 16, wherein before said solidification step, said spinning dope solution is extruded at a temperature of from 60° to 150° C. 
     
     
       18. The process as claimed in claim 16, wherein said evaporation is carried out at a temperature of from 60° to 400° C. 
     
     
       19. The process as claimed in claim 14, wherein said coagulation is carried out in two or more stages. 
     
     
       20. The process as claimed in claim 1, wherein said drawing temperature is 250° C. or more.